PURPOSE: To perform the cleaning of the interior surfaces easily and quickly by fitting a heater on the top of a molded form which covers the top opening of the roaster casing and has a heat-resistant inorganic material as its primary constituent, and applying heat through said molded form at the time of cooking.

CONSTITUTION: For a molded form 6 having a heat resistant inorganic material as its primary constituent, a ceramic plate, for instance, is used. The heater 7 comprises a heater element such as nichrome wire, etc., and is buried in the heat insulating material 8 consisting of class fiber and then fixedly attached to the top of the ceramic plate of the molded form 6. The roaster door 9 covers the front opening of the roaster casing 5, comprising a glass window 10, a roaster handle 11 and a tray 12. This constitution facilitates the replacement processes, and, at the time of cooking, the entire interior space of the casing 5 can be heated adequately. Since there is no protrusion inside the casing 5, the cleaning becomes easy, and, as all the spattered liquid from the cooked foodstuff such as fish remains in the casing 5, it does not adversely affect the external heater.